The present invention relates to the control of hydraulic fluid flow through a restriction. More specifically, the present invention relates to the control of hydraulic fluid flow through a restriction using an electro-rheological fluid or a magneto-rheological fluid.
Numerous applications in the prior art require that hydraulic fluid flow through a restriction be controlled. The simplest type of control is to use a specific size of a restriction and/or a hydraulic fluid having a specific viscosity. More sophisticated methods involve the control for the size of the restriction in relation to some specified parameter. At one end of the spectrum of the specified parameter, the restriction will be at its smallest size and at the opposite end of the spectrum of the specified parameter, the restriction will be at its greatest size.
One application which utilizes a variable restriction is in a shock absorber or damper positioned within a vehicle suspension system. In general, the vehicle suspension system is provided to filter or isolate the vehicle body from irregularities in a road surface as well as to control body and wheel motion. The conventional non-intelligent suspension system includes a spring and a damping device such as a shock absorber in parallel to accomplish this purpose. The spring and damping device are positioned in parallel between the sprung mass and the unsprung mass of the vehicle.
The damping devices, such as shock absorbers and/or struts, are used in conjunction with conventional non-intelligent or passive suspension systems to absorb unwanted vibrations which occur during driving. To absorb these unwanted vibrations, the conventional damping devices or hydraulic actuators often include a piston which is located within a pressure tube and which is connected to the body of the vehicle through a piston rod. The pressure tube is connected to the vehicle""s suspension system. Because the piston is able to limit the flow of damping fluid within the working chamber of the pressure tube when the damper is telescopically displaced, the damper is able to produce a damping force which counteracts the vibration which would be otherwise transmitted directly from the vehicle""s suspension system to the vehicle""s body. The greater the degree to which the flow of damping fluid within the working chamber is restricted by the piston, the greater the damping forces which are generated by the damper. Thus, a small size for the restriction will generate a high damping force and a large size for the restriction will generate a low damping force.
Various types of adjustment mechanisms have been developed to generate variable damping forces in relation to the speed of the vehicle, the amplitude of the displacement of the damper, the acceleration of the damper, the weight of the vehicle as well as other operating characteristics of the vehicle. These adjustment mechanisms have mainly been developed to provide a relatively small or low damping characteristic during the normal steady state running of the vehicle and a relatively large or high damping characteristic during vehicle maneuvers requiring extended suspension movements. The normal steady state running of the vehicle is accompanied by small or fine vibrations of the unsprung mass and thus, the need for a soft ride or low damping characteristic of the suspension system to isolate the sprung mass from these small vibrations. During a turning or braking maneuver, as an example, the sprung mass of the vehicle will attempt to undergo a relatively slow and/or large movement or vibration which then requires a firm ride or a high damping characteristic of the suspension system to support the sprung mass and provide stable handling characteristics to the vehicle. The adjustable mechanisms for the damping rates of the shock absorber typically function by controlling the amount of fluid flow between the various chambers of the shock absorber. The adjustable mechanisms offer the advantage of a smooth steady state ride by isolating the high frequency/small amplitude excitations of the unsprung mass while still providing the necessary damping or firm ride for the suspension system during vehicle maneuvers causing low frequency/large excitations of the sprung mass.
The continued development of shock absorbers includes the development of adjustment systems which provide the vehicle designer with a continuously variable system which can be specifically tailored to a vehicle to provide a specified amount of damping in relation to various monitored conditions of the vehicle and its suspension system.
The present invention provides the art with a controlled restriction for a hydraulic fluid flow passage. For exemplary purposes only, the controlled restriction is illustrated in conjunction with a shock absorber for a vehicle. The control of the size of the restriction and the amount of fluid flow through the passage is through the use of an electro-rheological fluid or a magneto-rheological fluid restriction which is disposed within the fluid passage. The amount of fluid flow through the restriction is controlled by applying an electric or magnetic field in a specified direction. The application of the electric or magnetic field and its direction in relation to the fluid flow will determine the amount of restriction and thus the amount of fluid flow.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.